1. Field of the Invention
The subject invention relates to switched-mode power supplies.
2. Description of the Related Art
Switched-mode power supplies generally include a power device for periodically applying power to a primary winding of a transformer. To this end, a main current path of the power device is connected in series with the primary winding and a source of power. In order to minimize dissipation on the power device, it is desirable that the power device be turned on when the voltage on the drain of the power device is at its minimum. This usually requires the measurement of the drain voltage, where voltages as high as 650 V. may be present, depending upon the application. Measuring such a high voltage is usually difficult and requires costly components.